Acromegaly is a hormonal disorder resulting from excess secretion of growth hormones from a pituitary gland caused by pituitary adenoma and the like. The affected patients have hypertrophy of heads, bones in hands and feet and soft tissues. The prevalence of acromegaly is about 60 patients per 1 million people, which is not necessarily high. However, the disease impacts the lives of the patients due to aberrations in parts of the body and is a serious disease having an increased risk of mortality because of cardiac diseases which occur in one-third of the patients.
Patients with acromegaly are currently treated by, in addition to surgical excision of adenoma secreting growth hormone and radiotherapy, drug therapy for exogenously administering an analogue of somatostatin, a hormone which suppresses secretion of growth hormone. Somatostatin analogues include octreotide acetate (Sandostatin®) by Novartis Pharmaceuticals and lanreotide acetate (Somatuline®) by Ipsen Pharma S.A.S., of which usefulness has been recognised and assured. Meanwhile the drugs are peptide drugs and thus require administration by injection, and it is reported that intramuscular injection of the sustained-release formulation thereof once in a few weeks is accompanied by significant pain. In order to solve the problem, it is believed to be the best choice to obtain a non-peptidic, orally administrable low-molecular compound rather than a peptide drug that requires injection.
Meanwhile, it has been revealed that there are 5 somatostatin receptor subtypes, SSTR1 to SSTR5, and it is reported that octreotide acetate and lanreotide acetate bind to somatostatin receptor subtype 2 (SSTR2) with high affinity. It has also been reported that the drugs bind to somatostatin receptor subtype 3 (SSTR3) and somatostatin receptor subtype 5 (SSTR5) with moderate affinity and do not bind to somatostatin receptor subtype 1 (SSTR1) or somatostatin receptor subtype 4 (SSTR4).
As the difference in affinity of octreotide acetate and lanreotide acetate towards the receptor subtypes has been scientifically revealed, a few non-peptidic, low-molecular somatostatin receptor agonists have been synthesised.
For example, PTL 1 discloses that the compound represented by the general formula (A):

wherein BA and DA independently represent a carbon or a nitrogen; AA and FA independently represent CH or a nitrogen, provided that only two or less of AA, BA, DA and FA are simultaneously nitrogen; R1A and R1aA independently represent a hydrogen, a C1-12 alkyl or the like; R2A represents a hydrogen, a C1-12 alkyl or the like; R3A and R4A independently represent a hydrogen, a halogen, a C1-12 alkyl or the like; R5A represents a (CH2)mA C6-10 aryl or a (CH2)mA C5-10 heterocyclyl; R6A represents a hydrogen, a halogen, CN or the like; R7A represents a hydrogen, a halogen, a C1-6 alkyl or the like; mA is an integer of 0 to 6; and xA is an integer of 1 to 3;
and a pharmaceutically acceptable salt, ester, enantiomer, diastereomer or a mixture thereof (the definitions of respective groups are abstracted) is a SSTR2-specific agonist and is useful for treatment of diabetes and related lesions (retinopathy, neuropathy, nephropathy, etc.).
NPL 1 discloses that the compound represented by the following formula (B):

has SSTR2 agonistic activity and suppresses secretion of growth hormone by systemic administration and suppresses ophthalmic angiogenic lesions by local administration.
In addition, PTL 2 discloses that the compound represented by the general formula (C):

wherein R1C represents a linear or branched (C1-C16)alkyl group, an alkenyl group, an alkynyl group or the like; R2C represents a group represented by —C(YC)NHX1C, —C(O)X2C or —SO2X3C; YC represents an oxygen atom or a sulphur atom; R3C represents a hydrogen atom, an alkyl group which may be substituted, an alkenyl group, an alkynyl group, an aralkyl group which may be substituted, a heteroarylalkyl group which may be substituted or the like; X1C represents a linear or branched (C1-C15)alkyl group, an alkenyl group, an alkynyl group or the like; X2C represents a linear or branched (C1-C10)alkyl group, an alkenyl group which may be substituted with a phenyl group or the like; X3C represents a linear or branched (C1-C10)alkyl group, an alkenyl group which may be substituted with a phenyl group or the like;
or an addition salt thereof with a pharmaceutically acceptable inorganic or organic acid (the definitions of respective groups are abstracted) shows a preferable affinity towards somatostatin receptors and is particularly useful for treating pathological conditions and illness in which somatostatin receptors are involved.
NPL 2 discloses that the 3-thio-1,2,4-triazole compound represented by the following formula (D):

is an SSTR2 and SSTR5 agonist.
Further, PTL 3 discloses that the compound having a pyridine-piperidine skeleton represented by the following formula (E):

wherein WE, XE and YE respectively and independently represent CH, C(R4E) or N; ZE represents C(R6E) or N; R1E and R2E respectively and independently represents a hydrogen atom or a C1-6 alkyl; R3E and R4E respectively and independently represent a halogen or a group selected from a C1-6 alkyl, a C1-6 alkoxy, a carbocycle and a heterocycle, any of which may be substituted with 1 to 5 RaE groups; when ZE is C(R6E), R5E represents a hydrogen atom, CN, —N(R6E) R7E, —C(O)N(R7E) R8E or the like; R6E represents a hydrogen atom, a C1-6 alkyl or the like; R7E and R8E respectively and independently represent a hydrogen atom or a group selected from a C1-6 alkyl which may contain 1 to 3 hetero atoms, a carbocycle and a heterocycle, any of which may be substituted with 1 to 5 RaE groups; each RaE independently represents a halogen, trifluoromethyl, oxo, —N(RbE)RcE, RdE or the like; RbE and RcE respectively and independently represent a hydrogen or RdE; RdE is selected from a hydrocarbon, a carbocycle, a carbocycle-C1-6 alkyl or a heterocycle, any of which may be substituted with 1 to 5 substituents selected from a halogen, cyano, hydroxy and the like; mE and nE respectively and independently represent 1 to 3;
is a compound inhibiting Wnt signalling.
However, none of the background art documents disclose the compound described herein, a salt thereof, an N-oxide thereof or a solvate thereof, or a prodrug of the foregoing, or pharmaceutical use thereof, which may not be deduced from any combination of background art documents.